1. Field of the Invention
The invention is directed to a drive and braking arrangement for a motor vehicle having at least one electric motor which drives the motor vehicle in dependence on the setting of an accelerator pedal, a forward/reverse drive direction selector which adjusts the driving direction of rotation of the electric motor or electric motors, means for detecting the driving speed of the motor vehicle, and a friction brake arrangement acting on at least one wheel of the motor vehicle.
2. Description of the Prior Art
Motor vehicles whose wheels are driven by electric motors, which are known, for example, from "VDI-Berichte", No. 878, 1991, pages 611 to 622, can be prevented from rolling backward on inclined roadways by the electric motors by means of depressing the accelerator pedal in a manner similar to conventional motor vehicles with automatic transmissions. Since the electric motors must be able to apply the driving moment preventing the motor vehicle from rolling backward in the stationary state, a comparatively high current passes through the motor which can lead to overheating and destruction of the electric motors.
It is known from DE-A-32 38 196 to prevent motor vehicles with automatic transmission from "creeping" during idling by means of an automatic auxiliary brake. The automatic auxiliary brake has an actuating drive which actuates the brake system of the motor vehicle and is set to a braking position when the driving speed lies below a limiting value close to zero and the brake pedal and accelerator pedal are not actuated. The auxiliary brake is released when actuating the gas pedal and/or brake pedal.
Further, an auxiliary brake for a motor vehicle with a conventional mechanical drive train is known from DE 39 09 907 A1. This auxiliary brake automatically assumes a braking position as soon as the actual rotating direction of the wheel does not correspond to the selected drive gear of the gear shift and is automatically released as soon as the rotating direction of the wheel matches the selected drive gear. This improves comfort as the auxiliary brake is actuated, i.e. applied or released, automatically without any effort on the part of the driver as soon as the motor vehicle is in a parking or driving situation requiring the application or release of the auxiliary brake. For this purpose, the motor vehicle is outfitted with:
an internal combustion engine driving the vehicle via an automatic transmission as a function of the position of the accelerator pedal, PA1 a forward/reverse gear selector, PA1 means for detecting the speed of the vehicle, PA1 an auxiliary brake acting on the wheels of one axle, PA1 an actuating drive for adjusting the braking force of the auxiliary brake, and PA1 an electronic control unit which actuates the actuating drive in the manner described above.